Windows can be evaluated for potential energy savings by looking at the age of the window, condition of the window (cracks, broken seals, missing panes), thickness of the glass (single pane, double pane, triple pane), and functionality of the window (fixed, sliding, awning). If existing windows show significant heat loss you may want to consider upgrading to more energy efficient windows. Low cost solutions to leaky windows include installing window films or weather-stripping to reduce air infiltration.
Doors can be evaluated in the same manner as windows with the exception that the heat loss will depend on the type of door (wood, steel, or glass). Insulated steel doors tend to have the highest insulation levels. Properly installed weather-stripping and door sweeps are also good areas for energy savings. Cracked or missing weather-stripping should be replaced to reduce air infiltration into the building.
Roof and wall insulation should be checked to see what the existing insulation levels are. If insulation levels are much lower than existing codes or there are missing or poor insulation levels throughout the building, the addition or replacement of insulation may reduce building heat loss.